The present invention relates to equipment for producing thin-walled and transparent plastic containers having a high impact resistance by orientation-blowing polyethylene terephthalate.
In ordinary blow molding processes, the upper and lower parts of an extruded parison are held by a mold and compressed air is blown into the thus held parison to radially expand the same for forming it into a container or the like product.
In such processes, however, since the parison is oriented only uniaxially, the resultant products are inevitably inferior in their strength or transparency. Accordingly, a so-called orientation-blow molding process in which a parison is oriented both laterally and longitudinally produces a blow-molded container having an increased strength and toughness as well as improved gas impermeability and transparency. The orientation-blow molding can be roughly divided into an extrusion blow molding process using an extruded parison and an injection blow molding process using an injected parison. The extrusion blow molding process is rather complicated because it requires more steps including pipe extrusion, cooling and cutting to obtain a cold parison, reheating of the parison, top and bottom forming, longitudinal orientation, and blowing. While, the injection blow molding is relatively simple because it contains a less number of steps such as parison injection, cooling, reheating, longitudinal orientation, and blowing. The present invention is based on the latter process, namely, injection blow molding.